Reactions of epoxides (n → σ*)

The primary mode of activation in chiral Lewis acid-catalyzed epoxide opening is polarization of the C-O σ-bond of the epoxide by coordination of a Lewis acid to the nonbonding electron pairs on the oxygen. Binding of the epoxide to the chiral Lewis acid activates the ring toward nucleophilic opening and places the enantiotopic carbons of the meso-epoxide within proximity to the influence of the chiral ligand on the Lewis acid. This chapter details the applications of chiral, nonracemic Lewis bases in the enantiodifferentiating reactions. In a detailed study on the mechanism of phosphoramide-catalyzed epoxide openings with SiCl4, Denmark and coworkers address questions regarding the stoichiometry, reaction kinetics, nonlinear effects, and the mode of activation for phosphoramide Lewis bases with SiCl4. The epoxide opening with SiCl4 produces an alkoxytrichlorosilane that can be susceptible to further Lewis base activation, leading to a dialkoxydichlorosilane and so forth.